The present invention relates to a power source off delay timer for use in an electric control device, and more particularly relates to such a power source off delay timer which times a certain time period after a power source has become shut off and then outputs a signal or the like.
A certain type of power source off delay timer is per se known which controls a keep relay. Such a power source off delay timer, when a power source is shut off, starts timing a certain time period of for example 0.5 seconds to 10 minutes, and at the end of this time period resets the keep relay. Now, it is convenient for a user of the power source off delay timer to be able ocularly to determine what is the current state of the device, i.e. to monitor it, and accordingly some visual indication of operation state is desirable. It might be conceived of to use a monitor lamp for displaying the operation state, and in such a case the lamp should be illuminated during the time that the power source is on and also during the time interval that the power source off delay timer is operating, between the time point at which the power source has turned off and the later time point that the power source off delay timer resets the keep relay. However, after the power source has turned off, the system must operate by using power stored in a capacitor or the like until the resetting of the keep relay, and the electrical power consumption of such a monitor lamp is too great for it to be operated by power stored in a capacitor for any reasonable time. This means that with the use of such a monitor lamp the time period which the power source off delay timer can time after the power source turns off is very limited, and for this reason the use of a monitor lamp in this type of power source off delay timer construction is virtually impracticable.
Accordingly, in a conventional power source off delay timer, for monitoring purposes it has been practiced to use a physical indicator such as a colored plate, which is moved in synchronization with the operation of the keep relay. In such a power source off delay timer, as one possible construction, the movement of a red indicator plate is coupled to the operation of the keep relay, and when the keep relay is in the set condition then the red indicator plate is in a position to be visible through a display window, whereas on the other hand when the keep relay is moved to the reset condition then the red indicator plate is moved and is hidden and thus is not in a position to be visible through said display window. Thus, the operational state of the device can be monitored by the operator by watching the display window.
However, in this type of construction, it is necessary to incorporate a linkage motion mechanism in the power source off delay timer for moving the colored plate in synchronization with the setting and the resetting of the keep relay. This causes the inconvenience that the mounting position of the keep relay becomes restricted, and also the mounting position of the display window becomes restricted. Thus, often, the keep relay cannot be mounted in a convenient position from the viewpoint of its operation, and also the display window cannot be placed in a position in which it is easily visible. Further, in this type of mechanical display device construction, a display which attracts the attention of the operator in a dynamic fashion, such as by periodic flashing or the like, cannot be provided.